The invention relates to an un-cooled infrared (IR) detector arrays having improved thermal stability and reduced fixed-pattern noise. More particularly, the invention relates to an IR detector array utilizing the output signals of blind reference detectors for canceling unwanted signal anomalies from the image signal generated by the IR detector array.
Various infrared radiation detectors are available in today""s electronics industry. Many techniques for converting infrared radiation to visible images, are also known.
One such radiation detection device is an infrared imaging device based upon photon-to-electron conversion. These devices can be extremely sensitive; however, a parallel process of thermal generation of electrons can produce significant detector noise. Consequently, photoelectric devices need to be cooled for effective use for infrared imaging. This leads to the use of dewars and cooling devices that add significant weight, bulk, and energy consumption to the imager.
Thermal detectors, in contrast to photoelectric detectors, do not need to be cooled since they convert the broadband heat absorbed directly into some measurable signal. A significant gap exists, however, between the performance of the best of the current generation of un-cooled IR imagers and that of cooled sensors. These xe2x80x9cun-cooledxe2x80x9d detectors are limited by the ability to thermally isolate them from their surroundings, by the amount of noise they introduce in their detection process, and by the readout noise introduced by electronics. With sufficient thermal isolation and reduced sensing noise, the sensitivity of thermal detectors can approach or even exceed that of photoelectric converters without the need for the mass, volume, and power required for cooling.
An exemplary un-cooled thermal detector which would benefit from such noise reduction is the bi-material micro-cantilever device increasingly utilized in the art. These devices bend, or deflect, when infrared radiation is absorbed upon an infrared responsive absorber element. The infrared radiation heats the bi-material section of the micro-cantilever, thereby urging one of the bi-materials to expand at a greater rate than the other bi-material, causing the micro-cantilever to deflect, or bend with respect to the substrate. The corresponding change in capacitance of the cantilever, relative to the substrate, produces a signal that is detected.
The signal is detected by an arrangement of a fixed reference capacitor and the variable cantilever capacitor forming a charge divider which, when sampled forms a voltage that is proportional to the cantilever capacitance. As can be appreciated the signal is susceptible to thermal drift and instabilities, and, since the signal is the result of minute changes of the cantilever temperature, accurate device temperature control is critical.
Accordingly, there is a need for an uncooled IR detector array having improved temperature stability and reduced fixed pattern noise.
The present invention is embodied in an infrared radiation detector array including a plurality of infrared radiation detectors having infrared radiation responsive elements. Each one of the plurality of infrared radiation detectors provides a proportionate electrical signal in response to infrared radiation incident thereto. A blind infrared radiation detector having a radiation responsive element is provided and shielded from the incident infrared radiation applied to the radiation detector array. The blind infrared radiation detector provides a proportionate electrical signal in response to infrared radiation incident thereto. In this way, the blind infrared radiation detector is configured such that its signal represents thermal distortion of the infrared radiation detector array.
According to one aspect of the invention, at least one blind infrared radiation detector and a scanning shift register provides an image signal of reduced fixed pattern noise and temperature stability. The scanning shift register selects one of the infrared radiation detectors which is read out and used to compensate the image sensing radiation detector.
According to another aspect of the invention, an image signal is provided of reduced fixed pattern noise and temperature stability by a first plurality of infrared sensors arranged in rows and columns. Each one of the plurality of infrared sensors has a deflectable micro-electromechanical infrared responsive element, for providing a proportionate electrical signal in response to infrared radiation incident thereto. A second plurality of blind infrared sensors arranged about a portion of the perimeter of the rows and columns. Each one of the second plurality of infrared sensors has a deflectable micro-electromechanical infrared responsive element. The radiation responsive elements of the second plurality of blind infrared sensors being shielded from incident infrared radiation representing the image for providing a proportionate electrical signal in response to infrared radiation incident thereto.
According to another aspect of the invention, an image signal is provided of reduced fixed pattern noise and temperature stability by the second plurality of blind infrared sensors which are positioned along at least one side perimeter of the rows and columns.